Frequency chirp of semiconductor lasers is a critical parameter for both analog and digital communications system performance. Prior art techniques for measuring chirp utilize a self-heterodyne method where a gated RF current is used to modulate a semiconductor laser. An interferometer is used to convert the frequency modulated optical output into an amplitude-modulated signal, which is then measured with a photoreceiver and spectrum analyzer to ascertain the degree of chirp present in the laser. In particular, by gating the RF current with a period .tau. equal to twice the delay associated with the interferometer, the modulated and unmodulated signals will mix together to generate a frequency chirp signal that can be observed by the spectrum analyzer.
Although this technique is well-accepted by the industry and provides accurate results, a separate test set including an interferometer is required to perform the analysis. The need for the test set thus adds to the production cost (and time) of the laser.